1. Field of the Invention
The present invention relates to a display device of top emitting type and a method for production thereof.
2. Description of the Related Art
Among recent flat panel display devices attracting attention is the organic EL display device which displays images by means of organic EL (Electro Luminescence). The organic EL display device is a wide viewing angle and a low electric power consumption, the former being due to the fact that it utilizes emission from organic EL elements themselves. In addition, being highly responsive to high-definition high-speed video signals, the organic EL display device is expected to find practical use in the field of image technology. It is also attracting attention because it will find use as a flexible device if it is formed on a flexible plastic substrate that permits the organic emitting material to exhibit its inherent flexible properties.
The organic EL display device employs the driving system of either active matrix type or passive matrix type. The former, which employs TFT (Thin film Transistors) as driving elements, is superior to the latter in responsiveness and resolving power. Therefore, it is considered to be suitable particularly to the organic EL display device having the above-mentioned characteristics. The organic EL display device of active matrix type has organic EL elements (each including an organic emitting layer) and a driving panel on which are arranged driving elements (or TFT mentioned above) to drive the organic EL elements. To the driving panel is bonded (with an adhesive layer) a sealing panel so that they hold the organic elements between them. Each organic EL element has an organic emitting layer formed between a pair of electrodes.
The organic EL display device falls under bottom emission type and top emission type. The former permits each organic EL element to emit light through the driving panel mentioned above. The latter permits each organic EL elements to emit light through the sealing panel mentioned above. The latter is becoming the mainstream of development because of its larger aperture ratio.
Meanwhile, the organic EL display device of top emission type is constructed such that the electrodes on the sealing panel (through which light emerges) are common to every organic EL element. The electrodes are made of an optically transparent conductive material such as ITO (Indium Tin Oxide). Unfortunately, ITO has a higher resistivity than ordinary metallic materials by two to three orders of magnitude. The high resistivity causes the applied voltage to fluctuate over the electrode through which light emerges. This deteriorates the quality of display.
To tackle this problem, there has been proposed in Japanese Patent Laid-open No. 2002-318556 (hereinafter referred to as Patent Document 1) a technology to form an auxiliary wiring that connects with the electrode through which light emerges, the auxiliary wiring being formed at the same level as the electrode and from the same material as the electrode on the driving panel.